The architecture of a Long Term Evolution (LTE) system is shown in FIG. 1. In LTE the downlink is based on orthogonal frequency division multiplexing (OFDM) while the uplink is based on a single carrier modulation method known as discrete Fourier transform spread OFDM (DFT-S-OFDM, see 3GPP TR 36.300, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Overall description; Stage 2, V8.2.0. In FIG. 1 the LTE architecture is shown including the logical interfaces between the radio base stations eNBs (X2) and between eNB and MME/S-GW (S1).
Uplink Power Control Loop in LTE
Typically, in a communication system, e.g., UTRAN and E-UTRAN, an open-loop power control mechanism is used in the uplink. This is also often supplemented with a closed-loop part which is not described herein. A common power control loop employed in communication systems, e.g., LTE see 3GPP TS 36.213. E-UTRA; Physical layer procedures, is given by:PSD=P0×PLα [W/Hz]  (Equation 1)
where:                PSD is the power spectral density of the Uplink (UL) transmission        P0 is the desired received power density        PL is the path loss, including shadowing and antenna gains        α is the path loss compensation fraction, where                    α=1 gives fair performance with optimum cell edge performance (full path loss compensation)            α<1 trading cell edge performance for higher cell throughput                        
P0 is a parameter, which can be composed of the sum of a cell specific nominal component and a UE specific component. As such it is possible to adjust P0 for the individual UEs within one cell.
Network Management
In FIG. 2 an exemplary management system is shown. The node elements (NE), also referred to as eNodeB (E-UTRAN) or NodeB (UTRAN), are managed by a domain manager (DM), also referred to as the operation and support system (OSS). A DM may further be managed by a network manager (NM). Two NEs can be interfaced by X2 in case of E-UTRAN, whereas the interface between two DMs is referred to as Itf-P2P.
A vision in the ongoing Evolved Universal Terrestrial Radio Access Network (E-UTRAN) standardization work is that the new system is self-organizing in as many aspects as possible, see e.g. NGMN, “Operator Use Cases related to Self Organising Networks,” ver. 1.53, 2007-04-16 and Third Generation Partnership Project (3GPP) technical Report TR 32.816, Study on Management of E-UTRAN and SAE.
One aspect that benefits from self-organization is automatic cell outage compensation. In current wireless communication systems there are situations when a whole base station or part of the base station (e.g. a sector/cell of a sectorized base station) is in outage due to hardware/software failures. When in outage the cell/base station cannot support any users in its vicinity and if these users cannot connect to another base station in the neighborhood then a coverage hole is created. For the operators of wireless access networks this is an undesirable consequence as potential revenue is missed from the unsupported traffic and also customer satisfaction is damaged.
Common practice today is that the wireless operators aim at repairing the malfunctioning cell/base stations as soon as possible (thereby restoring the original coverage).
As set out above conventional network managements systems can generate coverage “holes” in the event of a cell/sector outage. This is undesired as potential revenue is missed from the unsupported traffic and also customer satisfaction is damaged. This is particularly critical for services with a negotiated quality such as a guaranteed bit rate.
Also U.S. Pat. No. 5,852,778A “Method and system for providing communications service to a coverage hole” describes a communications service to a coverage hole in a DS-CDMA cellular communication system involving an OMC determining the configuration of the transmitters in adjacent cells to the coverage hole. The OMC then selects at least one, but less than all of the transmitters to increase power of a pilot channel.
The method described in U.S. Pat. No. 5,852,778A is gross grained and can cause interference problems. Hence, there exist a need for an improved method and a system that automatically can compensate for an outage in a cellular radio system.